Starting between 12 and 16 weeks pregnant, 350 women from a variety of ethnic and socioeconomic backgrounds took 400 IU, 2,000 IU or 4,000 IU of vitamin D per day until delivery.
Only those who took 4,000 IU of vitamin D per day achieved and sustained the desired level for themselves and baby at birth. There were no adverse events at any dose.
Doctors currently think the optimal range for circulating vitamin D is 20 to 60 ng/ml.